What is linear expansitivity

The magnetic field inside a superconducting solenoid is 4.50 t. the solenoid has an inner diameter of 6.20 cm and a length of 26.0 cm. determine (a) the magnetic energy density in the field and (b) the energy stored in the magnetic field within the solenoid.

Positrons are spontaneously emitted from the nuclei of

Sort the images based on whether there's a force of attraction or repulsion between the magnets shown. attraction repulsion